1. Field of the Invention
This invention relates to a table capable of tilting motion, more particularly, to a tilting rotary table device for subjecting a workpiece secured thereon to machining or scribing.
2. Description of the Prior Art
A conventional tilting rotary table device comprises a worm, which is rotatably disposed on a fixed base and provided with a handle at one end thereof, and a sector wheel, which is formed on the bottom frame of a tilting rotary table member and engaged with the worm. Such a device is adapted to set the tilting rotary table member rotatably supported on the fixed base to a desired inclination.
In a tilting rotary table device using such a worm gearing mechanism, however, shifts of the center of gravity of the workpiece secured on the table when the inclination is set cause the meshing part of the worm gearing to receive a part of the diagonal component of the load, thereby causing elastic strain and error in the set position of inclination. The mode of occurrence of error varies not only according to the magnitude of the table load and the inclination, but also according to the variation of cutting force as well as the variation of cutting direction. Furthermore, in cutting operations in which the loading direction is repeatedly reversed or in tilting operations in which the inclination of the table is changed, the change of the center of gravity of the workpiece secured on the table causes error in the inclination of the table corresponding to the backlash between the worm and the worm wheel.
Accordingly, the accuracy of engagement between the worm and the worm wheel of the worm gearing, the decisive factor behind accuracy of inclination of the tilting table, has had to be improved. This has been done through high precision machining and careful examination and selection of materials. Nevertheless, it has become increasingly difficult to attain satisfactory accurate inclination. This is because of the increasingly heavier, thereby larger, tables being used and the increasingly greater work loads. These have made the working surfaces of the worm gearing more susceptible to wear. This wear results in increased backlash in the worm gearing, causing error in the set inclination greater than tolerance.
Mechanical table tilting operations using worm gearing further require increased torque for operating the worm gearing along with increased table loads. Further, when a motor is employed to rotate the worm, the speed of the worm shaft varies, making the smooth control of the table tilting operation difficult.